Midified the headers and class definition to avoid circular dependencies

Added 2 methods to compute the divergence of the VectorField either to return the whole divergence field or just at a requested location

Updated the computation of laplacian of individual components of a VectorField using the scalar method previously defined

Added methods for the scalar 2D field to compute gradient and laplacian

Created the velocity projection function. Placed all the steps (diffusion, Poisson and projection) in a temporal loop

Added a function to solve the Poisson equation for the Pressure

Added the diffusion of the second component which was forgotten

Added the printing of the index when reaching out of bound state for debugging

Replaced the = operator for VectorField2D to return references, supposed to be better for efficiency

Added a getter to get the name of a scalar field

Added an advance_diffusion function, as well as the needed calculation of the laplacian of u and v in a vector field

Added get_dx and get_dy methods

Fixed the out of bound checking in get_index to include a missing value

Added a VectorField2D method to impose lid driven boundary conditions. Not very modular so shoud be changed in the future.

Simplified the constructor to take into account a default initial value